THE PHYSIOLOGY OF THE HEARTBEAT 195 



place where the wave arrives earliest. Somewhat different results are 

 obtained from the left ventricle, but again they are dependent upon the 

 relationship of the part to the Purkinje fibers (Fig. 55). A further dis- 

 cussion of the manner of spread of the impulse in the ventricles will be 

 found in the chapter devoted to interpretation of the electrocardiogram 

 (page 270). 



FIBRILLATION OF THE HEART 



Ventricles 



The even spread of the wave of contraction over the heart depends on 

 the uniform excitability of the muscular fibers. If certain of the muscu- 

 lar fibers, or bundles of fibers, have a greater or less excitability than 

 others, then, when the stimulus to contract arrives, it will not produce 

 a uniform contraction of neighboring bundles, and coordinated action of 

 the cardiac musculature will give place to a confused movement in which 

 each part of the heart is contracting independently of the rest. This 

 fibrillation, or delirium cordis, as it is called, can be produced by a large 

 variety of experimental methods, such, for example, as by stimulating 

 the ventricles with induced electric shocks, or by ligation of a large 

 branch of the coronary artery, or by the injection of lycopodium spores 

 into the coronary circulation, *or by mechanical stimulation of the heart 

 in the region of the auriculoventricular bundle. 



Fibrillation of the ventricles is undoubtedly a common cause of death 

 in man, for of course the confused movements make the ventricles in- 

 capable of contracting on the contents of the heart. It is a condition 

 which can probably never be recovered from in the higher animals, but 

 it is of interest that the ease with which it is set up as the result of the 

 application of an electric stimulus varies to a marked degree in differ- 

 ent animals, and that in those hearts in which fibrillation can be elic- 

 ited only with difficulty, recovery can usually be effected either by stop- 

 ping the heart by means of cold and then allowing it to beat again, or 

 by the administration of epinephrine. Of the hearts investigated in 

 this way, that of the rat has been found to be most resistant to stimula- 

 tion; then in order come those of the rabbit, the cat, the dog, and the 

 horse. There is good reason to believe that the heart of man is readily 

 affected. Fibrillation of the ventricle is undoubtedly the main cause of 

 death in most cases of electrocution. Curiously enough, however, it has 

 been stated that, whereas, a current of ordinary intensity (2300 volts 

 alternating current) produces ventricular fibrillation in the heart of cer- 

 tain of the lower animals, at least in that of the horse, a very much 

 stronger current does not do so, and may indeed cause ventricular fibril- 



